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Man’s Impact The following are some of man’s activities that can affect a habitat by starting a negative chain reaction within the food webs. 1. Land development 2. Farming 3. Pollution 4. Introducing invader species 5. Poaching Development As we build to improve our life, wetland, prairie, and forest habitats are destroyed and animals are displaced. These animals move into the surrounding habitat causing the different populations to increase. This increase in population will cause more competition for food. If the carrying capacity of the habitat is exceeded, some of the animals will starve and die. Plants can’t move so they will die. Nature can impact a habitat too Floods and fires cause the same type of chain reaction as development. Drought causes the same chain reaction as the low levels of dissolved oxygen after an algae bloom. When a dam is built across a river to make a lake, it will cause the same type of chain reaction as other development because the habitat will be under water. Channelization is when a curving (meandering) river is made to flow in a straight line. This speeds up the flow of the water. It will also make the water muddier. This causes the same type chain reaction as development because it changes the animals habitat. Farming Practices We spray herbicides to kill unwanted plants. We spray pesticides to kill unwanted insects. We put fertilizer on plants to make them grow faster and bigger. All three of these practices are done to get larger yields from the crops we grow. This is a good thing . The problem occurs when we use too much. Herbicides Herbicides can enter a wetland, pond or river after heavy rains. (runoff) 1. The first thing that happens is some of the plants will die. 2. This will cause an increase in the competition for food between any of the animals that eat these plants. 3. Some of the animals that eat plants may starve and die because there is less food. 4. Fewer first level consumers will effect the next level consumers and so on. Pesticides Pesticides can enter a wetland, pond or river after heavy rains. (runoff) 1. The first thing that happens is some of the insects will die. 2. This will cause an increase in the competition for food between any of the animals that eat these insects. 3. Some of the animals that eat insects may starve and die because there is less food. 4. Fewer second level consumers will effect the next level consumers and so on. Fertilizer Fertilizer can enter a wetland, pond or river after heavy rains. (runoff) 1. The first thing that happens is an increase in plant growth called an algae bloom. 2. When the extra food from the fertilizer runoff is used up, some of the surplus plants will die. 3. As the decomposers (bacteria) break down these dead plants they will use up the dissolved oxygen in the water. 4. The lower levels of oxygen will cause some of the fish to die. 5. This will cause an increase in the competition for food between any of the animals that eat these fish. 6. Some of the animals that eat fish may starve and die because there is less food. 7. Fewer second level consumers will effect the next level consumers and so on. More Farming Practices Overgrazing is when livestock eats to much of the vegetation in an area. Overgrazing of a prairie can cause the same chain reaction as development. Feedlots contain a large number of animals in a small area. These animals create a large amount of waste. If this waste runs off into a wetland, pond or river it can cause a chain reaction just like fertilizer runoff. Planting fescue (a type of grass) in a prairie changes the diversity of the habitat from hundreds of different types of plants to a single type of plant. This will cause a chain reaction similar to development. More problems caused by man Sewage (human waste) from septic tanks or waste water treatment plants can have the same affect on wetlands, ponds and rivers as fertilizer runoff . Oil kills some plants and animals and makes it hard for others to stay in the habitat. Chlorine is used to kill microscopic plants and animals in the water. Invader Species Invader species are not native to Missouri habitats. 1. They compete with the native species for food and space. 2. If this new species is more successful, the native population of plants or animals may decrease. Causing a chain reaction in the food webs of a habitat. Examples: Zebra mussels compete with native mussels in a river or lake. Crayfish compete with the native crayfish. Asian carp compete with the native fish. Invader Species continued Gypsy moth larvae will eat the leaves of a tree. This will cause the tree to make more leaves instead of seeds. It also causes the tree to use up some of its winter reserves which will stress the tree and possibly cause it to die. Purple loosestrife competes with the native plants in a wetland. Musk thistle competes with native plants in a prairie. Illegal Hunting Poachers taking any animal in large numbers will have a negative effect on the food webs of a habitat. Lead shot in ducks can have an impact on the birds of prey in a food web. Lead is toxic. DDT in a food chain For many years, the chemical DDT was used to kill certain insects that carry human diseases and attack crops. Then scientists found that DDT harmed other organisms in food chains. The figure above shows how DDT became more concentrated in animals’ bodies as it moved through a food chain. Birds and fish with high levels of DDT could not reproduce successfully, and their populations decreased. In 1972, the government banned the use of DDT. Why does DDT become more concentrated as it passes up a food chain?